diff --git a/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs b/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
index e3e78c6575..c0cc9a8dd6 100644
--- a/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
+++ b/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
@@ -695,11 +695,7 @@ loop e = do
               SyncV2.handleSyncFromFile description syncFileSrc projectBranchName
             SyncFromCodebaseI srcCodebasePath srcBranch destBranch -> do
               description <- inputDescription input
-              let srcBranch' =
-                    srcBranch & over #project \case
-                      Nothing -> error "todo"
-                      Just proj -> proj
-              SyncV2.handleSyncFromCodebase description srcCodebasePath srcBranch' destBranch
+              SyncV2.handleSyncFromCodebase description srcCodebasePath srcBranch destBranch
             ListDependentsI hq -> handleDependents hq
             ListDependenciesI hq -> handleDependencies hq
             NamespaceDependenciesI path -> handleNamespaceDependencies path
diff --git a/unison-cli/src/Unison/Codebase/Editor/HandleInput/SyncV2.hs b/unison-cli/src/Unison/Codebase/Editor/HandleInput/SyncV2.hs
index df5a2480a3..f34a64302a 100644
--- a/unison-cli/src/Unison/Codebase/Editor/HandleInput/SyncV2.hs
+++ b/unison-cli/src/Unison/Codebase/Editor/HandleInput/SyncV2.hs
@@ -57,13 +57,15 @@ handleSyncFromCodebase description srcCodebasePath srcBranch destBranch = do
           branch <- MaybeT (Q.loadProjectBranchByName (project ^. #projectId) srcBranchName)
           lift $ Project.getProjectBranchCausalHash branch
       case maySrcCausalHash of
-        Nothing -> pure $ Left (error "Todo proper error")
+        Nothing -> pure $ Left (Output.SyncFromCodebaseMissingProjectBranch srcBranch)
         Just srcCausalHash -> do
           let shouldValidate = True
-          fmap (const srcCausalHash) <$> liftIO (SyncV2.syncFromCodebase shouldValidate srcConn codebase srcCausalHash)
+          Right . fmap (const srcCausalHash) <$> liftIO (SyncV2.syncFromCodebase shouldValidate srcConn codebase srcCausalHash)
 
   case r of
-    Left _err -> pure $ error "Todo proper error"
-    Right (Left syncErr) -> Cli.respond (Output.SyncPullError syncErr)
-    Right (Right causalHash) -> do
+    Left openCodebaseErr -> Cli.respond (Output.OpenCodebaseError srcCodebasePath openCodebaseErr)
+    Right (Left errOutput) -> Cli.respond errOutput
+    Right (Right (Right causalHash)) -> do
       Cli.setProjectBranchRootToCausalHash (projectBranch ^. #branch) description causalHash
+    Right (Right (Left syncErr)) -> do
+      Cli.respond (Output.SyncPullError syncErr)
diff --git a/unison-cli/src/Unison/Codebase/Editor/Input.hs b/unison-cli/src/Unison/Codebase/Editor/Input.hs
index 684a5ac1ea..c496b5ba0d 100644
--- a/unison-cli/src/Unison/Codebase/Editor/Input.hs
+++ b/unison-cli/src/Unison/Codebase/Editor/Input.hs
@@ -128,7 +128,7 @@ data Input
   | PushRemoteBranchI PushRemoteBranchInput
   | SyncToFileI FilePath (ProjectAndBranch (Maybe ProjectName) (Maybe ProjectBranchName))
   | SyncFromFileI FilePath UnresolvedProjectBranch
-  | SyncFromCodebaseI FilePath UnresolvedProjectBranch UnresolvedProjectBranch
+  | SyncFromCodebaseI FilePath (ProjectAndBranch ProjectName ProjectBranchName) UnresolvedProjectBranch
   | ResetI (BranchId2 {- namespace to reset it to -}) (Maybe UnresolvedProjectBranch {- ProjectBranch to reset -})
   | -- | used in Welcome module to give directions to user
     --
diff --git a/unison-cli/src/Unison/Codebase/Editor/Output.hs b/unison-cli/src/Unison/Codebase/Editor/Output.hs
index 13c0a076cc..6b5f528869 100644
--- a/unison-cli/src/Unison/Codebase/Editor/Output.hs
+++ b/unison-cli/src/Unison/Codebase/Editor/Output.hs
@@ -35,6 +35,7 @@ import U.Codebase.Sqlite.ProjectReflog qualified as ProjectReflog
 import Unison.Auth.Types (CredentialFailure)
 import Unison.Cli.MergeTypes (MergeSourceAndTarget, MergeSourceOrTarget)
 import Unison.Cli.Share.Projects.Types qualified as Share
+import Unison.Codebase (CodebasePath)
 import Unison.Codebase.Editor.Input
 import Unison.Codebase.Editor.Output.BranchDiff (BranchDiffOutput)
 import Unison.Codebase.Editor.Output.BranchDiff qualified as BD
@@ -43,6 +44,7 @@ import Unison.Codebase.Editor.RemoteRepo
 import Unison.Codebase.Editor.SlurpResult (SlurpResult (..))
 import Unison.Codebase.Editor.SlurpResult qualified as SR
 import Unison.Codebase.Editor.StructuredArgument (StructuredArgument)
+import Unison.Codebase.Init.OpenCodebaseError (OpenCodebaseError)
 import Unison.Codebase.IntegrityCheck (IntegrityResult (..))
 import Unison.Codebase.Path (Path')
 import Unison.Codebase.Path qualified as Path
@@ -442,6 +444,8 @@ data Output
     -- ephemeral progress messages that are just simple strings like "Loading branch..."
     Literal !(P.Pretty P.ColorText)
   | SyncPullError (Sync.SyncError SyncV2.PullError)
+  | SyncFromCodebaseMissingProjectBranch (ProjectAndBranch ProjectName ProjectBranchName)
+  | OpenCodebaseError CodebasePath OpenCodebaseError
 
 data MoreEntriesThanShown = MoreEntriesThanShown | AllEntriesShown
   deriving (Eq, Show)
@@ -681,6 +685,8 @@ isFailure o = case o of
   IncoherentDeclDuringUpdate {} -> True
   Literal _ -> False
   SyncPullError {} -> True
+  SyncFromCodebaseMissingProjectBranch {} -> True
+  OpenCodebaseError {} -> True
 
 isNumberedFailure :: NumberedOutput -> Bool
 isNumberedFailure = \case
diff --git a/unison-cli/src/Unison/CommandLine/InputPatterns.hs b/unison-cli/src/Unison/CommandLine/InputPatterns.hs
index f2fc24cf7d..40a82c2241 100644
--- a/unison-cli/src/Unison/CommandLine/InputPatterns.hs
+++ b/unison-cli/src/Unison/CommandLine/InputPatterns.hs
@@ -773,6 +773,23 @@ handleBranchWithOptionalProject =
         otherNumArg -> Left $ wrongStructuredArgument "a project branch" otherNumArg
     )
 
+handleBranchWithProject :: I.Argument -> Either (P.Pretty CT.ColorText) (ProjectAndBranch ProjectName ProjectBranchName)
+handleBranchWithProject =
+  either
+    ( \str ->
+        Text.pack str
+          & tryInto @(These ProjectName ProjectBranchName)
+          & first (const $ expectedButActually' "a project branch" str)
+          >>= \case
+            These project branch -> pure $ ProjectAndBranch project branch
+            That _branch -> Left $ expectedButActually' "a project branch" str
+            This _project -> Left $ expectedButActually' "a project branch" str
+    )
+    ( \case
+        SA.ProjectBranch (ProjectAndBranch (Just proj) branch) -> pure $ ProjectAndBranch proj branch
+        otherNumArg -> Left $ wrongStructuredArgument "a project branch" otherNumArg
+    )
+
 mergeBuiltins :: InputPattern
 mergeBuiltins =
   InputPattern
@@ -2192,7 +2209,7 @@ syncFromCodebase =
             ]
         ),
       parse = \case
-        [codebaseLocation, branchToSync, destinationBranch] -> Input.SyncFromCodebaseI <$> unsupportedStructuredArgument makeStandalone "a file name" codebaseLocation <*> handleBranchWithOptionalProject branchToSync <*> handleBranchWithOptionalProject destinationBranch
+        [codebaseLocation, branchToSync, destinationBranch] -> Input.SyncFromCodebaseI <$> unsupportedStructuredArgument makeStandalone "a file name" codebaseLocation <*> handleBranchWithProject branchToSync <*> handleBranchWithOptionalProject destinationBranch
         args -> wrongArgsLength "three arguments" args
     }
   where
diff --git a/unison-cli/src/Unison/CommandLine/OutputMessages.hs b/unison-cli/src/Unison/CommandLine/OutputMessages.hs
index 6b8c8a279a..2285c9b727 100644
--- a/unison-cli/src/Unison/CommandLine/OutputMessages.hs
+++ b/unison-cli/src/Unison/CommandLine/OutputMessages.hs
@@ -65,6 +65,7 @@ import Unison.Codebase.Editor.Output.PushPull qualified as PushPull
 import Unison.Codebase.Editor.SlurpResult qualified as SlurpResult
 import Unison.Codebase.Editor.StructuredArgument (StructuredArgument)
 import Unison.Codebase.Editor.StructuredArgument qualified as SA
+import Unison.Codebase.Init.OpenCodebaseError qualified as CodebaseInit
 import Unison.Codebase.IntegrityCheck (IntegrityResult (..), prettyPrintIntegrityErrors)
 import Unison.Codebase.Patch qualified as Patch
 import Unison.Codebase.Path qualified as Path
@@ -974,6 +975,7 @@ notifyUser dir = \case
       --       defs in the codebase.  In some cases it's fine for bindings to
       --       shadow codebase names, but you don't want it to capture them in
       --       the decompiled output.
+
         let prettyBindings =
               P.bracket . P.lines $
                 P.wrap "The watch expression(s) reference these definitions:"
@@ -2264,6 +2266,31 @@ notifyUser dir = \case
     case syncErr of
       Sync.TransportError te -> pure (prettyTransportError te)
       Sync.SyncError pullErr -> pure (prettyPullV2Error pullErr)
+  SyncFromCodebaseMissingProjectBranch projectBranch ->
+    pure . P.wrap $
+      "I couldn't sync from the codebase because the project branch"
+        <> prettyProjectAndBranchName projectBranch
+        <> "doesn't exist."
+  OpenCodebaseError codebasePath err -> case err of
+    CodebaseInit.OpenCodebaseDoesntExist ->
+      pure . P.wrap $ "I couldn't find a valid codebase at " <> prettyFilePath codebasePath
+    CodebaseInit.OpenCodebaseUnknownSchemaVersion schemaVersion ->
+      pure . P.wrap . P.lines $
+        [ "I couldn't open the codebase at " <> prettyFilePath codebasePath <> ".",
+          "The schema version appears to be newer than the current UCM version can support.",
+          "You may need to upgrade UCM. The codebase is at schema version: " <> P.shown schemaVersion
+        ]
+    CodebaseInit.OpenCodebaseFileLockFailed -> do
+      pure . P.wrap . P.lines $
+        [ "I couldn't open the codebase at " <> prettyFilePath codebasePath,
+          "It appears another process is using that codebase, please close other UCM instances and try again."
+        ]
+    CodebaseInit.OpenCodebaseRequiresMigration currentSV requiredSV ->
+      pure . P.wrap . P.lines $
+        [ "I couldn't open the codebase at " <> prettyFilePath codebasePath,
+          "The codebase is at schema version " <> P.shown currentSV <> " but UCM requires schema version " <> P.shown requiredSV <> ".",
+          "Please open the other codebase with UCM directly to upgrade it to the latest version, then try again."
+        ]
 
 prettyShareError :: ShareError -> Pretty
 prettyShareError =
diff --git a/unison-runtime/src/Unison/Runtime/Interface.hs b/unison-runtime/src/Unison/Runtime/Interface.hs
index dfa54e01e4..e8e1442836 100644
--- a/unison-runtime/src/Unison/Runtime/Interface.hs
+++ b/unison-runtime/src/Unison/Runtime/Interface.hs
@@ -1440,18 +1440,19 @@ buildSCache crsrc cssrc cacheableCombs trsrc ftm fty int rtmsrc rtysrc sndbx =
     restrictTyR m = Map.restrictKeys m typeRefs
 
 standalone :: CCache -> Word64 -> IO StoredCache
-standalone cc init = readTVarIO (combRefs cc) >>= \crs ->
-  case EC.lookup init crs of
-    Just rinit ->
-      buildSCache crs
-        <$> readTVarIO (srcCombs cc)
-        <*> readTVarIO (cacheableCombs cc)
-        <*> readTVarIO (tagRefs cc)
-        <*> readTVarIO (freshTm cc)
-        <*> readTVarIO (freshTy cc)
-        <*> (readTVarIO (intermed cc) >>= traceNeeded rinit)
-        <*> readTVarIO (refTm cc)
-        <*> readTVarIO (refTy cc)
-        <*> readTVarIO (sandbox cc)
-    Nothing ->
-      die $ "standalone: unknown combinator: " ++ show init
+standalone cc init =
+  readTVarIO (combRefs cc) >>= \crs ->
+    case EC.lookup init crs of
+      Just rinit ->
+        buildSCache crs
+          <$> readTVarIO (srcCombs cc)
+          <*> readTVarIO (cacheableCombs cc)
+          <*> readTVarIO (tagRefs cc)
+          <*> readTVarIO (freshTm cc)
+          <*> readTVarIO (freshTy cc)
+          <*> (readTVarIO (intermed cc) >>= traceNeeded rinit)
+          <*> readTVarIO (refTm cc)
+          <*> readTVarIO (refTy cc)
+          <*> readTVarIO (sandbox cc)
+      Nothing ->
+        die $ "standalone: unknown combinator: " ++ show init
diff --git a/unison-share-api/src/Unison/SyncV2/Types.hs b/unison-share-api/src/Unison/SyncV2/Types.hs
index 419918e107..2f4432ee74 100644
--- a/unison-share-api/src/Unison/SyncV2/Types.hs
+++ b/unison-share-api/src/Unison/SyncV2/Types.hs
@@ -165,8 +165,7 @@ newtype Version = Version Word16
   deriving stock (Show)
   deriving newtype (Eq, Ord, Serialise)
 
-data StreamInitInfo
-  = StreamInitInfo
+data StreamInitInfo = StreamInitInfo
   { version :: Version,
     entitySorting :: EntitySorting,
     numEntities :: Maybe Word64,